Deforming Grease Pencil Strokes in 3D
There's a new UI method intended for this (see below) but I find that the standard binding workflow actually works. In Object Mode, create a Grease Pencil object. Next Create an Armature object, and use Edit Mode to make whatever adjustments are needed to get them to line up as desired. Next, in Object Mode, select the Grease Pencil object, and Shift-select the Armature object, and from the Parenting menu (Ctrl-P), choose to bind with Automatic Weights. The Grease Pencil object will follow the bones.



The new UI for doing this is in Edit Mode for the stroke itself. First, create an Armature modifier for the Grease Pencil object, and point it to the Armature to be bound, as a target. Then in Edit Mode for the stroke, from the Grease Pencil Menu, go to Weights > Generate Weights > With Automatic Weights. 



I assume these methods are the same and don't know why you would choose between them. But I think it's easier to use the old method.